Multicast communication method in a CDMA mobile communication system

ABSTRACT

A multicast communication method in a CDMA mobile communication system which is capable of reducing a transmission power in a base station system, and is capable of performing an efficient multicast operation for a large number of mobile subscribers is provided. The starting of information distribution by a multicast operation and identification information indicating a content of the information thereof are notified through a broadcast channel to a mobile subscriber. Further, through the broadcast channel, information such as a spread code or the like to be used at this time, which is necessary for actual reception of communication data, is notified. Then, in the mobile subscriber, a surround environment of the mobile subscriber is checked to determine the possibility of simultaneous receiving from a plurality of other base station systems. If possible, similar notified information is also received from other base station systems. Thus, all kinds of information regarding the spread code or the like to be used for receiving distributed information are obtained.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a division of application Ser. No. 11/357,985, filedFeb. 22, 2006, now pending, which is a continuation of application Ser.No. 10/397,524, filed Mar. 27, 2003, now abandoned, which is acontinuation of application Ser. No. 09/456,377, filed Dec. 7, 1999, nowU.S. Pat. No. 6,542,755, issued Apr. 1, 2003, and based on JapanesePatent Application No. 10-347549, filed Dec. 7, 1998, by TsutomuTSUKAGOSHI, all of which are incorporated herein by reference in theirentirety. This application claims only subject matter disclosed in theparent applications and therefore presents no new matter.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multicast communication method to beperformed in a CDMA (Code Division Multiple Access) mobile communicationsystem.

2. Description of the Related Art

As a conventional multicast communication method in the CDMA mobilecommunication system, Japanese Patent Laid-Open Hei 10 (1998)-107770discloses a multicast communication method in which service negotiationsfor the multicast communication is performed in a calling procedurebetween a mobile subscriber (abbreviated as MS, hereinafter) and a basestation system (abbreviated as BSS, hereinafter) for the MS obtaining aspread code to be used for each multicast communication method.

Alternatively, in a plurality of BSSs, each multicast service data hasbeen transmitted by using a broadcast channel of each BSS without anylinkage to one another.

However, the following problems were inherent in the foregoingconventional multicast communication method in the CDMA mobilecommunication system.

(1) Regarding a system where a spread code is allocated for eachmulticast communication method by service negotiations in a callingprocedure between the MS and the BSS, since a registration operation forthe spread code is executed for each multicast service in MS thatreceives information, processing becomes complex. Thus, the system isnot suitable for the multicast communication method of advertising usewhere information is simultaneously transmitted to a large number of MS.In addition, since the spread code must be fixed for each multicastcommunication method to be notified, dynamic use of limited number ofspread codes is not allowed. Thus, this system lacks efficiency.

(2) Regarding a system where each multicast communication data istransmitted by each BSS by using respective broadcast channels, sincethe position of MS cannot be specified when a multicast operation isperformed, transmission power in each BSS must be set to a maximum inorder to enable possible MS located in the vicinity of a boundary toreceive a signal sent from BSS. But if signal for data is transmitted byan output more than necessary, noises are generated in other MS.Consequently, a capacity of the entire system is reduced.

The present invention was made in order to solve the foregoing problemsinherent in the prior art, and it is an object of the invention toprovide a multicast communication method in a CDMA mobile communicationsystem, which is capable of reducing transmission power in BSS andperforming an efficient multicast operation for a large number of MS.

SUMMARY OF THE INVENTION

In order to achieve the foregoing object, in accordance with an aspectof the present invention, a multicast communication method in a CDMAmobile communication system, which comprises a plurality of mobilesubscribers, a plurality of base station systems connected to the mobilesubscribers by radio channels, a plurality of mobile switching centersconnected to the base station systems and a multicast communicationserver connected to the mobile switching centers for providinginformation to be distributed to the mobile subscribers, the method ischaracterized in that each of the base station systems transmitinformation which is necessary for enabling the mobile subscriber toreceive the multicasting information through respective broadcastchannels to each of the mobile subscribers before multicastinginformation is transmitted.

The method comprises:

(1) sending a multicast request to at least one anchor base stationsystem together with area information for multicasting;

(2) instructing a multicast request from the anchor base station systemto at least one branch base station system necessary for coveringmulticasting area indicated by the area information;

(3) transmitting multicast starting information and spread code to beused for multicasting information to mobile subscribers throughrespective broadcast channels of the anchor base station system and thebranch base station system; and

(4) transmitting multicasting information from the anchor base stationsystem and the branch base station system after proper time interval,during which the mobile subscribers have been ready for receivingmulticasting information, has been elapsed.

The multicast communication method set forth above, wherein the anchorbase station system uses a diversity hand-over trunk for establishinglinks to the branch base station systems.

The multicast communication method set forth above, wherein the methodfurther comprises receiving multicasting information, at the mobilesubscriber, transmitted from a plurality of base station systems, andperforming a RAKE combine process for respective received signals.

In another aspect, the method comprises:

(1) sending a multicast request to at least one anchor base stationsystem together with area information for multicasting;

(2) instructing a multicast request and link establishment request fromthe anchor base station system to at least one branch base stationsystem necessary for covering multicasting area indicated by the areainformation;

(3) sending back information of link establishment completion andinformation of decided spread code for multicasting information at eachbase station system to the anchor base station system from the branchbase station system,

(4) transmitting multicast starting information together with a listindicating base station systems transmitting identical multicastinginformation and spread code to be used for multicasting information tomobile subscribers through respective broadcast channels of the anchorbase station system and the branch base station system; and

(5) transmitting multicasting information from the anchor base stationsystem and the branch base station system after proper time interval,during which the mobile subscribers have been ready for receivingmulticasting information, has been elapsed.

The multicast communication method in a CDMA mobile communication systemset forth above, wherein the method further comprises:

(6) detecting, at the mobile subscriber, receivable base station systemslisted in the list transmitted through the broadcast channel, andpreparing reception of multicasting information by setting spread codesindicated in said list; and

(7) receiving multicasting information, at the mobile subscriber,transmitted from a plurality of base station systems, and performing aRAKE combine process for respective received signals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an embodiment of a multi-cast communicationmethod in a CDMA mobile communication system according to the presentinvention.

FIG. 2 is a view showing a specific example of a configuration includingMS, BSS and MSC shown in FIG. 1.

FIG. 3 is a view illustrating a flowchart of a multicast communicationmethod operation in the CDMA mobile communication system shown in FIGS.1 and 2.

FIG. 4 is a view illustrating another flowchart of a multicastcommunication method operation in the CDMA mobile communication systemshown in FIGS. 1 and 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the present invention will be described withreference to the accompanying drawings.

FIG. 1 shows an embodiment of the CDMA mobile communication system inwhich the multicast communication method of the present invention isperformed.

As shown in FIG. 1, the embodiment comprises a plurality of mobilesubscribers (MSs 1 and 2), base station systems (BSSs 3 to 6) connectedto the MSs 1 and 2 by radio channels for playing main roles ofinformation multicasting to the MSs 1 and 2, mobile switching centers(MSCs 7 and 8) connected to the BSS 3 and also connected to the BSSs 4to 6 for processing calls originated from the MSs 1 and 2 or callsincoming thereto, updating location information of the MSs 1 and 2, agateway mobile switching center (G-MSC 9) connected to the MSCs 7 and 8for performing connections to other networks, a multicast communicationserver 10 connected to the G-MSC 9, and also another multicastcommunication server 11 connected to the MSCs 7 and 8. Radio connectionsbetween the MS1 and the BSS 3, and between the MSs to the BSSs 4 to 6are respectively established by a mobile communication procedure usingthe CDMA system.

The multicast communication servers 10 and 11 store contents informationof multicast services, area information of each multicast service as adestination for multi-casting information, and time for multicastinginformation. Timers are installed inside of server. These timers are setfor each stored information, and by the timers, time for startingmulticasting the stored information can be detected. Further, a serviceidentifier is set for each multicast service so as to enable distributedinformation to be identified in the MSs 1 and 2.

FIG. 2 shows a specific example of the embodiment composed of the MS2,the BSSs 4 to 6 and the MSC 8 shown in FIG. 1.

As shown in FIG. 2, BSSs are classified into an anchor BSS 5 for playingmain roles of information multi-casting, and branch BSSs 4 and 6 forsubordinately contributing to information multicasting by means of linkconnection between each branch BSS and the anchor BSS 5. The anchor BSS5 and branch BSSs 4 and 6 are connected to each other by links 18 and19.

Functional sharing between the anchor BSS and the branch BSSs may bedifferent for each multicast information. Also, even for identicalinformation, functional sharing may be different for each multicastinginformation, for example between day and night.

The BSSs 4 to 6 respectively include diversity hand-over trunk (DHT) 12to 14 provided to perform a soft hand-over operation in the CDMA system,and radio sections 15 to 17 provided to perform radio signaltransmission and reception processing, and signal modulation anddemodulation. The soft hand-over operation is one of unique features ofthe CDMA system. As the CDMA system uses the same frequency for radiocommunication, a MS can establish a plurality of radio channels to aplurality of BSSs as long as radio signal condition is good for eachBSS. Therefore, as for the reverse channel signal, the BSS 5 can receivesignal from the MS 2 not only via the radio section 15 of own BSS butalso via the radio section 16 of the BSS 4 and the radio section 17 ofthe BSS 6, and the strongest signal is selected as the received signalat the DHT 12 in the BSS 5.

The area information to be transmitted, which has been stored in themulticast communication servers 10 and 11, contains bits of informationregarding which BSS should be set as an anchor BSS and which BSS shouldbe set as a branch BSS. The area information may be different for eachmulticasting information. For G-MSc 9 and MSCs 7 and 8, a different BSSconfiguration may be specified each time a multicast transmissionrequest is transmitted. For example, even for identical multicastinformation, area information different between day and night may bespecified.

In order to perform communications between BSSs 3 to 6 and MSs 1 and 2,the mobile communication system includes a broadcast channel provided tosimultaneously inform system information or the like to a plurality ofMSs, and a traffic channel provided to transmit specific data mainly torespective MS. MSs 1 and 2 include means provided to enable individualbroadcast channel reception to be performed.

Next, a multicast communication method in the mobile communicationsystem configured in the foregoing manner will be described.

FIG. 3 illustrates a flowchart of an embodiment of a multicastcommunication method in the CDMA mobile communication system shown inFIGS. 1 and 2.

First, in the multicast communication server 10 or 11, when a time comesto transmit accumulated data, information to be transmitted is notifiedtogether with area information to be transmitted to G-MSC 9 or MSCs 7and 8, and a request is made to perform a multicast operation (step S1).Here, if G-MSC 9 receives a request transmitted from the multicastcommunication server 10 or 11, the request is transferred to MSCs 7 and8 corresponding to the requested area information. In G-MSC 9, thisrequest is copied when necessary, and transferred to a plurality ofMSCs.

On the other hand, if MSCs 7 and 8 receive a request transmitted fromthe multicast communication server 10 or 11, the request is transferredto the anchor BSSs 3 and 5 corresponding to the requested areainformation. In the MSCs 7 and 8, this request is copied when necessary,and transferred to a plurality of anchor BSSs.

Upon having received the request transferred from the MSC 8, the anchorBSS 5 hunts the DHT 12 for a multicast operation, and informs thestarting of information transmission to surrounding branch BSSs 4 and 6corresponding to the area for information transmission. Then, links 18and 19 are established for transmission of the notified informationbetween branch BSSs 4 and 6 (step S2).

Then, in the branch BSSs 4 and 6, information necessary for transmittinginformation regarding a spread code or the like at the time ofinformation transmission is selected and decided (step S3). A spreadcode may be different not only for performing a multicast operation fordifferent information, but also for transmitting identical informationat a different time. Then, in each of BSSs 4 to 6, the starting ofinformation transmission by the multicast operation is notified throughthe broadcast channel to subordinate MS 2 (step S4). At this time,identification information indicating the selected spread code,information for deriving the spread code or the spread code itself issimultaneously notified. Also, information other than the spread code,which is necessary for data reception by the MS 2, is notified.

After the starting of the multicast operation has been notified to theMS 2, with an appropriate time interval, data is transmitted from theanchor BSS 5 through the DHT 12 to the branch BSSs 4 and 6.Subsequently, in a branch BSS that has received the data transmittedfrom the BSS 5, a multicast operation is performed by using thepre-selected and decided spread code (step S5).

In the MSS 1 and 2, the broadcast channel has been received forreceiving the paging of an incoming call during waiting or systeminformation. Upon having received the starting of the multicastoperation through the broadcast channel, in the MSs 1 and 2, theidentification information indicating the spread code, the informationfor deriving the spread code or the spread code itself used forinformation transmission is received through the broadcast channel ofthe same BSS.

If the identification information indicating the spread code or theinformation for deriving the spread code is received, based on theinformation, the spread code is introduced, and setting is made for datareception based on the spread code. Also, information other than thespread code, which is necessary for data reception, is received.

In the MSs 1 and 2, after the starting of the multi-cast operation hasbeen recognized based on the information received through the broadcastchannel, in order to detect whether the same information is transmittedfrom surrounding BSSs, a receiving operation is also performed for thenotified information transmitted from another BSS. If the transmissionof the same information from another BSS is recognized, then setting ismade for data reception by the same procedure.

If MS can receive data from a plurality of BSSs, setting is made forperforming the RAKE combine.

(Other Embodiments)

FIG. 4 illustrates a flowchart of another embodiment of a multicastcommunication method in the CDMA mobile communication system shown inFIGS. 1 and 2.

First, in the multicast communication server 10 or 11, when a time comesto transmit accumulated data, information to be transmitted is notifiedtogether with area information to be transmitted to the G-MSC 9 or theMSCs 7 and 8, and a request is made to perform a multicast operation(step S11). Here, if the G-MSC 9 receives a request transmitted from themulticast communication server 10 or 11, the request is transferred tothe MSCs 7 and 8 corresponding to the requested area information. In theG-MSC 9, this request is copied when necessary, and transferred to aplurality of MSCs.

On the other hand, if the MSCs 7 and 8 receive a request transmittedfrom the multicast communication server 10 or 11, the request istransferred to the anchor BSSs 3 and 5 corresponding to the requestedarea information. In the MSCs 7 and 8, this request is copied whennecessary, and transferred to a plurality of anchor BSSs.

Upon having received the request transferred from the MSC 8, the anchorBSS 5 hunts the DHT 12 for a multicast operation, and informs thestarting of information transmission to surrounding branch BSSs 4 and 6corresponding to the area for information transmission. Then, links 18and 19 are established for transmission of the notified informationbetween branch BSSs 4 and 6 (step S12).

Subsequently, in the branch BSSs 4 and 6, information necessary fortransmitting information regarding a spread code or the like at the timeof information transmission is selected and decided, and transmitted tothe anchor BSS 5 (step S13). A spread code may be different not only forperforming a multicast operation for different information, but also fortransmitting identical information at a different time. Then, in theanchor BSS 5, the information transmitted from the branch BSSs 4 and 6is combined with the information for data transmission, such as thespread code selected and set in the anchor BSS 5. Then, a list of BSS towhich identical information is transmitted, and a list of informationregarding the spread code or the like used by each BSS, are made, andnotified to the branch BSSs 4 and 6 (step S14).

In the branch BSSs 4 and 6, when the starting of the multicast operationis notified, the list of BSS to which identical data is transmitted andthe list of information regarding the spread code or the like used byBSS are also notified simultaneously, these lists having been receivedfrom the anchor BSS 5. Also, in the anchor BSS 5, when the starting ofthe multicast operation is notified, the list of BSS to which identicaldata is transmitted and the list of information regarding the spreadcode or the like used by BSS are simultaneously notified (step S15).

After the information transmitted from the BSSs 4 to 6 have beenreceived, in the MS 2, detection is made as to existence of receivableBSS in the list of BSS to which received identical data is transmitted.If receivable BSS exists, then the information regarding the spread codeor the like used by BSS, which has been received beforehand, is used,and setting is made to receive data from a plurality of BSSs.

With a proper time interval from processing in step S15, in the anchorBSS 5, data is transmitted through the DHT 12 to the branch BSS5 4 and6. Then, in the BSS that has received the above data, a multicastoperation is performed for the data by using the setting of pre-selectedand decided spread code or the like (step S16)

Because of the foregoing configuration, the present invention iseffective in the following respects.

(1) Signals transmitted from a plurality of base station systems can becombined by performing the RAKE combine in a mobile subscriber locatingin the vicinity of the boundary of the cell. Accordingly, even iftransmission power is set low in one base station system, a signalstrength after RAKE combined in the mobile subscriber can be kept high.Thus, transmission power can be reduced in the base station system thatperforms a multicast operation.

(2) A multicast operation can be performed without any complexprocedures such as a calling operation. A multicast operation can beefficiently performed for a large number of mobile subscribers.

1. A mobile communication system, comprising: a multicast communicationserver; a gateway core node; a core node; a base station system; and amobile station, wherein: the multicast communication server isconfigured to transmit a request regarding a multicast communication tothe gateway core node; the gateway core node is configured to transmit arequest regarding the multicast communication to the core node afterreceiving the request transmitted from the multicast communicationserver; the core node is configured to transmit a request regarding themulticast communication to the base station system after receiving therequest transmitted from the gateway core node; the base station systemis configured to notify the mobile station of a starting of themulticast communication; and the mobile station is configured to performa data reception of the multicast communication by combining signalsfrom a plurality of base station systems.
 2. The mobile communicationsystem according to claim 1, wherein the mobile station receivesinformation about at least one neighboring base station system for thecombining signals from a plurality of base station systems.
 3. A controlmethod for a mobile communication system, the mobile communicationsystem comprising a multicast communication server; a gateway core node;a core node; a base station system; and a mobile station, the controlmethod comprising: transmitting, by the multicast communication server,a request regarding a multicast communication to the gateway core node;transmitting, by the gateway core node, a request regarding themulticast communication to the core node after receiving the requesttransmitted from the multicast communication server; transmitting, bythe core node, a request regarding the multicast communication to thebase station system after receiving the request transmitted from thegateway mobile core node; notifying, by the base station system, themobile station of a starting of the multicast communication afterreceiving the request transmitted from the core node; and performing, bythe mobile station, a data reception of the multicast communication bycombining signals from a plurality of base station systems.
 4. A controlmethod for a mobile communication system according to claim 3, furthercomprising receiving, by the mobile station, information about at leastone neighboring base station system for the combining signals from aplurality of base station systems.